Steering for such hydraulic jet propulsion units is commonly effected by swivelling the discharge nozzle or by deflecting the jetstream by a rudder or by deflectors. Reversing is commonly effected by diverting the water so that it issues from one or more forward facing nozzles or by deflecting the jetstream so that it is turned by substantially more than 90.degree. or by reversing the pumping means so as to reverse the flow of water. A neutral condition is commonly brought about by partial operation of the reversing means or by stopping the operation of the pumping means.
Known steering means and known reversing means commonly associated with hydraulic jet propulsion apparatus suffer from one or more of the following deficiencies:
(1) Excessive mechanical work is required to turn the jetstream through the necessary angle for steering. This may be caused by an unbalance of hydraulic forces exerted on the steering means. PA0 (2) The steering means is liable to jamming by debris which may pass through the jet propulsion apparatus. PA0 (3) Operation of the steering means reduces the propulsive efficiency of the apparatus. This may be caused by restriction of the cross-sectional area of the jetstream or by spillage such that a proportion of the flow of water flows in a direction contrary to the main stream or by turbulence created by the steering means. PA0 (4) The reverse thrust provided is inadequate to effectively control the vessel. This may be caused by inefficient turning of the jetstream or by spillage from a deflector device or by the inefficiency of the pumping means when operated with reverse rotation. PA0 (5) Steering is not effective in the neutral or in the reverse modes. This may be through lack of any provision for steering in one or both of these modes. PA0 (6) In the reversing mode a stream of water (or streams of water) flowing forwardly under the vessel carry entrained air which in turn is sucked into the pump of the propulsion apparatus and reduces the capacity of the pump to discharge water. This reduces the effectiveness of the reversing means and causes an unnecessary increase in engine r.p.m.